Monocular and stereo monochrome night vision systems are in widespread use in law enforcement, military, and recreational applications. These traditional systems are sensitive to the visible and infrared spectrum, but during light gathering and photon scavenging within the microchannel plate (MCP) photomultiplier tube, all color information is lost, which leaves a monochrome image illuminated by the green P43 phosphor at the rear of the tube. The application of the green P43 phosphor is chosen primarily because of the human eye's sensitivity toward this wavelength due to peak gain. As well, green wavelengths are the least bright signal viewable by the human eye, which, in turn, creates energy efficiencies in the system while concurrently keeping the viewer night adapted.
This image composed of monochromatic shades of green, leaves viewers starved for color information. Since color perception is a key factor in situational awareness, a full-color night vision system is useful for distinguishing objects from a background and identifying them.
A number of techniques for color night vision have been proposed and implemented, but generally require complex and expensive mechanisms and imagers. One technique is to require three input/output channels to represent the color spectrum, typically RGB (red, green, and blue), increasing to an impractical six intensifiers for stereo color vision.
An alternative technique is to use a spinning wheel or other mechanical apparatus to rapidly change color filters at the entrance and exit of a single intensifier. Both techniques drive up the cost and complexity, with increased weight and bulk that is especially critical for head-worn goggles.
The additional complexity associated with these approaches has slowed the adoption of color night vision systems. Thus, while it would be possible to simply combine the existing stereo, monochrome techniques and monocular, color techniques to yield stereo, color night vision functionality, the resulting system would be so complex and cumbersome as to make field usage impractical.
Another major issue with all night vision systems is image noise. All image amplification tubes used in night vision devices have inherent noise, seen as a distinctive speckling or scintillation of individual pixels from frame to frame, becoming more prominent as the gain (amplification) and/or operating temperature is increased. In a low-light environment, the shot noise from random photon arrivals tends to dominate the image and preclude its interpretation. Small amounts of color channel noise can easily dominate the chrominance signal in real-world scenes.
Ideally, a color night vision system should adapt to changing luminance and scenic parameters such that it automatically presents an easily interpreted, accurate rendering of the scene. A practical system must be portable, rugged, and not overly costly.